Coating materials with low surface free energy are of great interest for many reasons. The low surface free energy provides liquid-repellent properties as well as anti-adhesion properties. For this reason, various systems have been developed, e.g. systems including PTFE as a low surface free energy polymer due to the presence of perfluorinated carbon chains or acrylic systems including perfluorinated carbon chain containing polymers. Sol-gel based systems have been developed on the basis of hydrolyzable silanes having perfluorinated side chains, and gradient coatings have been fabricated from these fluorosilanes. These materials are generally cured or hardened by thermal treatment resulting in the formation of Si—O—Si bonds. However, these systems based on an inorganic matrix are very sensitive to alkaline attack due to the low stability of the Si—O—Si bond at higher pH values.
When acrylic bonds capable of crosslinking are included, photocurable systems are obtained. However, the crosslinking degree upon formation of inorganic Si—O—Si bonds (inorganic condensation) is rather poor when the coatings are photocured so that the sensitivity to alkaline attack is still high. The addition of other organic polymeric compounds does not change this situation. This is because stable, highly condensed matrices containing Si—O—Si bonds require hardening at high temperatures which are generally not applicable to such polymers, as described in C. J. Brinker, G. W. Scherer: “Sol-Gel Science—The Physics and Chemistry of Sol-Gel-Processing”, Academic Press, Boston, San Diego, New York, Sydney (1990).
Photolithographic processes involving the systems described above also suffer from a poor alkali resistance. However, a high alkali resistance for low surface free energy coating is critical in order to be able to clean the surfaces with appropriate alkaline cleaners or to maintain a liquid-repellent surface even when contacting fluids of a higher pH. This problem is still unsolved for low surface free energy materials currently in use. Furthermore, liquid repellency coatings also having a high resolution and/or high aspect ratio pattern are not known.
Accordingly, it is an object of the present invention to provide a substrate having a liquid-repellent coating of high alkali resistance which can be used in pattern forming methods.
These and other objects are achieved in accordance with the invention by means of a cationically polymerizable composite coating composition comprising: a) a condensation product of at least one hydrolyzable silane having a fluorine-containing group, b) at least one cationically polymerizable organic resin, and c) a cationic initiator.